Properties of Nonwood Fibers*1

James S. Han*2

ABSTRACT

Nonwood or agro-based fibers are a potential source of pulping material. However, these fibers have tremendous variations in chemical and physical properties as compared to wood fiber. This study presents some chemical and physical properties of nonwood fibers derived from selected tissues of various monocotyledonous and dicotyledonous plants. Properties were compared for different fiber lengths at different growth stages and plant stalk heights.

1. INTRODUCTION

In general, fibers can be classified into three categories: wood, nonwood, and nonplant. The term “nonwood” was coined to distinguish plant fibers from the two main sources of wood fibers. hardwoods and softwoods. Non-wood or agro-based fibers are derived from selected tissues of various mono- or dicotyledonous plants (Parham & Kausftinen, 1974) and are categorized botanically as grass, bast, leaf, or fruit fibers. Some nonwood fibers are classified by means of production; fibers such as sugar cane bagasse, wheat straw. and corn stalks are byproducts. Other nonwood fibers are grouped as “fiber plants,” plants with high cellulose content that are cultivated primarily for the sake of their fibers such as jute, kenaf, flax, cotton. and ramie. Some fiber plants also produce useful byproducts; for example, oils from kenaf and flax seed. Nonwood fibers can be used to make paper, although the quality varies a great deal depending on the source of the fibers. Combining wood with nonwood fibers can reduce the amount of chemicals needed for pulping as well as shorten pulping time, thus saving energy. The high cellulose content of cotton linter (85% to 90%) compared to that of wood (35% to 49% cellulose) and the low lignin content of hemp (3%) make these nonwood fibers valuable for papermaking. Although there are some drawbacks to nonwood pulping, most nonwood fibers are bulky and vulnerable to biological deterioration during storage.

2. CHEMICAL PROPERTIES

Data reported on the chemical properties of nonwood fibers vary greatly. Studies have varied in fiber source, fiber age (growing time), and methodology. The data on the chemical composition of some common nonwood fibers shown in Table 1 were reported by Parham and Kausftinen (1974). Table 2 shows lignin composition of selected nonwood fibers compared to content of ash and selected

*1 Part of this paper was presented as Fiber Property Comparison at the TAPPI 1998 North American Nonwood Symposium at Atanata, GA, February 17~18 Co-sponsored by USDA Forest Service and USDA Biobased Products Coordination Council. *2 USDA Forest Service, Forest Products Laboratory, Madison, WI 53705-2398. USA The Forest Products Laboratory is maintained in cooperation with the University of Wisconsin. This article was written and prepared by U.S. Government employees on official time, and it is therefore in the public domain and not subject to copyright.

–3– Table 1. Chemical Composition of Some Common Non-wood fiber Compared to Wood Fiber. Chemical composition (% total) Fiber type Cellulose Lignin Pentosan Ash Silica

Stalk Rice 28~48 12~16 23~28 15~20 9~14 Wheat 29~51 16~21 26~32 4.5~9 3~7 Barley 31~45 14~15 24~29 5~7 3~6 Oat 31~48 14~19 27~38 6~8 4~6.5 Rye 33~50 14~19 27~30 2~5 0.5~4 Cane Sugar 32~48 19~24 27~32 1.5~5 0.7~35 Bamboo 26~43 21~31 15~26 1.7~5 0.7 Grass Esparto 33~38 17~19 27~32 6~8 - Sobai - 22 24 6 - Reeda 44~46 22~24 20 3 2 Bast Seed flax 43~47 21~23 24~26 5 - Kenaf 44~57 15~19 22~23 2~5 - Jute 45~63 21~26 18~21 0.5~2 Hemp 57~77 9~13 14~17 0.8 - Ramie 87~91 5~8 core Kenaf 37~49 15~21 18~24 2~4 - Jute 41~48 21~24 18~22 0.8 Leaf Abacab 56~63 7~9 15~17 3 - Sisalc 47~62 7~9 21~24 0.6~l Seed hulld 85~90 0.7~1.6 3~Jan 0.8~2 1 Wood Coniferous 40~45 26~34 7~14 < 1 - Deciduous 38~49 23~30 19~26 < 1 - Notes: a Phragmites communis, b Manila, c Agave. d Cotton linter.

sugars. In general, the higher the lignin content, the lower the cellulose content. Since cellulose is a homopolysaccharide composed of (-D-glucopyranose units linked together by (IR4)-glucosidic bonds and since only fractions of glucose units are expected to be derived from hemicellulose, high glucose content generally represents high cellulose content in chemical analysis. Nonwood hemicellulose is mostly arabinoglucuronoxylan and/or glucuronoxylan. Thus, a high percentage of xylose is an indication of high hemicellulose content. On the basis of xylose content, bagasse, coconut shell, purple top, and big bluestem have the highest hemicellulose content of the nonwood fibers listed in Table 2. More data on the chemical properties of nonwood, hardwood, and softwood fibers have been reported by Han and Rowell (1997). Chemical properties are influenced by fiber growth time(days after planting), botanical classification of fiber. and stalk height.

-4 - Table 2. Chemical Composition of Some Common Nonwood Fibers by Order of Decreasing Lignin Content Chemical composition (% total)a Fiber type Lignin Ash Glu Ara Gal Pha Xyl Man

Peat moss 45.90 1.10 19.16 0.25 2.54 1.19 2.77 2.35 Coconut shell 35.72 - 25.91 0.29 0.32 0.21 23.93 0 Cocount fiber 33.50 - 34.87 0.05 0.36 0.16 16.98 0.12 Sheet moss 30.20 11.50 18.46 1.37 5.44 1.24 1.34 7.27 Flax shive 27.80 - 34.89 0.28 0.73 0.32 18.50 1.99 Acacia 26.00 - 41.99 1.37 0.49 0.28 15.46 1.72 Jute core 24.77 0 39.09 0.11 0.41 0.38 17.35 0.91 Flax 22.90 - 31.21 1.17 1.77 0.62 12.29 1.13 Sunn hemp, core 22.74 0 41.46 0.26 0.73 0.27 17.08 1.94 Rice hull 21.40 16.30 33.89 1.52 0.85 0.05 13.95 0.16 Bagasse 19.87 0.25 43.10 1.93 0.55 0 24.019 0.18 Velvet leaf core 19.61 0 40.61 0.29 0.73 0.49 18.333 0.75 Spanish moss 19.50 1.90 29.54 4.61 4.86 0.23 15.04 0.72 Kudzu bark 19.30 36.55 2.93 2.04 0.54 4.95 1.09 Purple top 18.86 2.77 31.96 2.85 1.13 0.72 20.25 0.18 Little bluestem 18.79 2.41 35.05 3.03 1.18 0.12 18.19 0 Kenaf core 18.30 33.45 0.49 0.83 0.29 14.24 1.01 Big bluestem 18.17 2.48 34.19 2.88 1.20 0.27 19.57 0.20 Spagnum moss 16.60 1.90 29.54 4.61 4.86 0.23 15.04 0.72 Tobacco 16.46 0.53 33.16 0.63 0.80 0.472 12.40 0.92 Kudzu 15.70 - 39.40 1.81 1.67 0.57 11.36 0.69 Lechugilla 15.21 0 41.84 0.45 1.03 0.14 17.33 0 Loofa 13.60 - 56.38 0.24 0.36 0.15 14.89 0.17 Jute fiber 13.73 0.14 56.87 0.11 0.49 0.16 12.17 0.50 Hibiscus elantus 12.60 - 55.98 0.58 0.70 0.29 9.01 0.29 Abaca 12.66 0.19 52.69 1.83 1.03 0.16 12.81 0.89 Banana pinzota 11.10 1.20 43.24 3.85 1.47 0.34 10.66 1.82 Sunn hemp, base fiber 11.14 0.23 56.38 1.08 2.05 0.29 1.97 2.99 Kenaf 9.88 - 43.32 2.04 0.46 1.25 10.80 1.25 Tobacco bark 9.69 0 27.42 1.46 1.33 0.62 8.42 0.90 Velvet leaf 9.03 0.12 34.37 1.89 1.67 0.77 8.95 0.98 Agave cantala 6.80 0.23 55.79 0.42 1.24 0.46 12.83 0.82 Pineapple 4.60 0.10 64.35 0.90 0.71 0.06 12.04 0.20 Hesperaloe funifera 4.09 0.01 37.88 1.85 1.75 0.41 7.39 3.43 Hemp, Chinese 3.00 0.40 83.81 1.34 2.11 0.79 1.92 3.03 Hemp, degum 2.50 0.10 83.81 0.26 1.34 0.18 1.18 1.87 Notes: a L-arabinose(Ara), L-rhamnose(£f). L-galactose(gal), D-mannose(Man), D-glucose(Glu), D-xylose(Xyl)

2.1 Fiber Growth Time Using kenaf as the model. an intensive study was conducted on changes in chemical and physical properties of nonwood fibers as a function of fiber growth time. The results led to the conclusion that the vast differences between sets of data can be explained by differences in fiber growth time(Table 3) (Han & Rowell, 1995 · 1997). As the kenaf fiber matures, lignin. glucose. and xylose content increase and anbinose, galactose, rhamnose, and mannose decrease. The pattern of extractives content apparent in Table 3 also occurred for fiber length. We speculate that extractives content differs at early and later stages of fiber

-5 - Table 3. Chemical Composition of Kneaf Bast Fiber as Function of Fiber Growth time. Chemical composition (% ovendry basis) DAPa Extb Lignin Glu Am Gal Rha Xyl Man

35 14.87 4.32 28.86 3.95 0.78 2.72 6.54 1.76 42 8.80 6.00 33.20 3.18 0.62 1.82 7.31 1.63 57 5.13 8.32 35.45 2.21 0.55 1.46 8.08 1.59 63 4.34 7.74 37.08 2.43 0.62 1.48 8.61 1.53 70 4.63 8.70 40.53 2.02 0.46 1.25 9.37 1.47 77 4.99 9.23 40.52 2.05 0.39 1.36 9.16 1.34 84 5.07 8.33 39.88 2.27 0.49 1.63 9.39 1.53 91 5.68 9.38 42.82 1.91 0.42 1.35 9.98 1.31 98 2.42 8.81 41.60 2.13 0.48 1.73 9.69 1.35 133 8.03 8.94 41.98 1.67 0.48 1.15 9.72 1.31 155 7.83 9.99 46.39 1.27 0.38 0.87 11.20 1.19 161 11.51 10.22 39.22 2.54 0.56 1.52 9.75 1.33 168 12.31 9.74 41.41 2.18 0.47 1.37 10.36 1.39 175 8.23 9.69 49.33 1.40 0.36 0.87 12.29 1.02

Notes: a Days after planting, b Extractives.

Fig. 1. Kenaf ash content as a function of growing Fig. 2. Kenaf protein content as a function of growing time. time.

Fig. 3. Combined kenaf ash and protein content as a function of growing time.

growth. The ash and protein content of the kenaf was also measured as a function of fiber growth (Fig. I -3). Combined ash and protein in the kenaf core was as much as 27% at 49 days after planting (DAP) and as little as 7% at 175 DAP.

–6– The high protein content noticed early in the growth of kenaf is a fairly universal phenomenon in nonwood fibers. High protein content is believed to interfere with Klason lignin analysis. Since some types of protein are insoluble in acid, it is possible that the reported value for lignin could be higher than the actual value (TAPPI standard T-222). This problem in lignin analysis of nonwood fiber needs to be corrected in situations that warrant an equivalent of Klason lignin content.

2.2 Botanical Classification Core and bast fiber are the two major botanical classifications of plant fibers. Other botanical classifications are root and stalk fiber. The lignin content of kenaf is higher in the core than in the bast fiber. The higher concentration of lignin in the core compared to other parts of the plant is true for many annual plants (Table 4). Lignin concentration can be twice as much in the core as in other plant parts. This high lignin content of core fibers is one of the most important factors that affect pulping of nonwood fibers.

Table 4. Chemical Composition of Fiber by Botanical Classification. Chemical composition (%) Fiber type Botanical part Lignin Glu Ara Gal Rha Xyl Man Kenaf Stalk fiber 9.88 43.32 2.04 0.46 1.25 10.80 1.25 Root fiber 14.33 36.70 1.81 1.02 0.44 8.85 0.80 Stalk core 18.30 33.45 0.49 0.83 0.29 12.24 1.01 Root core 20.54 38.41 0.28 0.55 0.32 17.87 0.68 Velvet leaf Fiber 9.03 34.37 1.89 1.67 0.77 8.95 0.98 Core 19.61 40.61 0.29 0.73 0.49 18.33 0.75 Sunn hemp Fiber 11.14 56.38 1.08 2.05 0.29 1.97 2.99 Core 22.74 41.46 0.26 0.73 0.27 17.08 1.94 June Fiber 13.73 56.87 0.11 0.49 0.16 12.17 0.50 Core 24.77 39.09 0.11 0.41 0.38 17.35 0.91 Tobacco Fiber 9.69 27.42 1.46 1.33 0.62 8.42 0.90 Core 16.46 33.16 0.63 0.80 0.42 12.40 0.92

2.3 Stalk Height Chemical composition can also vary within the same part of a plant. Both root and stalk core have high lignin content than that of fiber. Since kenaf can grow quite tall. we studied whether chemical content differs in the top and bottom parts of the stalk. Samples from the top of the stalk had lower lignin content than did samples from the bottom (Table 5).

Table 5. Chemical Composition of Kenaf at Top and Bottom of Stalk at Various Growth Times. Chemical composition (%) DAP Stalk part Lignin Glu Ara Gal Rha Xyl Man 42 Top 5.00 32.65 2.50 1.74 0.82 7.04 1.72 42 Bottom 6.50 36.01 2.75 1.50 0.74 8.50 1.48 57 Top 5.10 30.61 3.11 1.96 0.68 6.78 2.02 57 Bottom 9.00 38.18 2.49 1.47 0.45 8.93 1.35 77 Top 4.10 27.53 3.99 2.83 0.73 5.90 2.00 77 Bottom 19.10 36.71 0.34 0.61 0.37 17.48 1.12

-7- 3. PHYSICAL PROPERTIES

A notable physical difference between wood and nonwood fiber is that nonwood fibers are formed in aggregates or bundles. This is why nonwood fibers like cotton and flax can be used to make rope and textile. The fiber aggregates are polymers, with a single fiber unit representing the basic building block of the polymer. Physical properties important to the understanding of non-wood fibers are fiber length and width, crystallinity, and permeability. Fiber length is the most important of the-se properties for pulping.

3.1 Fiber Length Knowledge about fiber length is important for comparing different kinds of nonwood fibers. The length and width of some common nonwood fibers are shown in Table 6 (Isenberg, 1967). More information on this topic has been published by Han and Rowell (1997). Maximum length and width of some pitted vessel elements of common nonwood fibers (Pfaffli & Sisko, 1995) are shown in Table 7. Fiber length is an important factor in pulping. Methodology for measuring wood fiber length and fiber length data were reported in detail by Isenberg (1967).

Table 6. Length and Width of Some Common Nonwood Fibers Fiber length (mm) Fiber width (mm) Common name (Scientific name) Avg Range Ave Range Ramie (Boehmeria nivea) 120 60~250 50 11~80 Flax (Linum usitatissimum) 33 9~70 19 5~38 Hemp (Cannabis sativa) 25 5~55 25 10~51 Ceiba, kapok tree (Ceiba pentandra) 19 8~30 19 10~30 Cotton lint(Gossypium spp.) 18 10~40 20 12~38 Paper-mulberry (Broussonetia papyrifera) 10 6~20 30 25~35 Sunn (Crotaria juncea) 8 4~12 30 25~50 Abaca (Musa textilis) 6 2~12 24 16~32 Kenaf (Hibiscus cannabinus) 5 2~6 21 14~33 Sidal (Agava Sislana) 3 1~8 20 8~41 Bamboo (Dendrocalamus arundinacea) 2.7 1.5~4.4 14 7~27 Raphia (Raphia hookeri) 2.4 - 30 17~46 Sabai (Eulaliopsis binata) 2.1 0.5~4.9 9 4~28 Common reed (Phragmites communis) 2.0 1.0~3.0 16 10~20 Jute (Corchrous caspsularis) 2 2~5 20 10~25 Papyrus (Cyperus papyrus) 1.8 1.0~4.0 12 8~25 Sugar cane (Sacchrum officiarum) 1.7 0.8~2.8 20 10~34 Corn (Zea mays) 1.5 0.5~2.9 18 14~24 Rice (Oriza sativa) 1.4 0.4~3.4 8 4~16 Wheat (Triticum sativum) 1.4 0.4~3.2 15 8~34 Esparto (Stipa tenacissima) 1.2 0.2~3.3 13 6~22 Albardine (Lygeum spartum) 1.1 0.2~3.1 12 6~21

3.2 Relationship of fiber length to fiber growth stage. Variation of wood fiber length can be expressed as a two-dimensional function of tree height and fiber distance from pith. We compared the fiber length of wood and nonwood fibers using red pine, aspen, and

-8- Table 7. Maximum Length and Width of Pitted Vessel Elements in Common Nonwood Fibers Common name (Scientific name) Max length(mm) Max width(mm) Raphia (Raphia hooker) 5.0 350 Oil palm (elaeis guineensis) 4.0 300 Sugar cane (Sacchrum officiarum) 2.1 200 Common reed (phragmites communis) 2.0 120 Papyrus (Cyperus papyrus) 1.7 100 Bamboo (Dendrocalamus strictus) 1.0 250 Wheat (Triticum sativum) 1.0 60 Sabai (Eulaliopsis binata) 1.0 50 Rice (Oriza sativa) 0.8 70 Albardine (Lygeum spartum) 0.7 30 Corn (Zea mays) 0.6 120 Esparto (Stipa tenacissima) 0.4 40

Fig. 4. Length of kenaf fiber at 147 days after Fig. 5. Length of kenaf fiber at 175 days after planting. planting.

Fig. 6. Average length of kenaf fiber at 147 and 175 days after planting.

kenaf samples as models. Data for red pine and aspen are shown in Tables 8 and 9, respectively; data for kenaf are shown in Fig. 4. Fibers at the center of a selected height were longer than outer fibers. and fibers at the top of the tree were shorter than those at the bottom. Kenaf stalk samples were taken at different growth stages(l47 and 175 DAP), and fiber length was measured every 12 inches(305mm). Fiber length gradually increased from the bottom to the top of the plant. Fiber length also increased as a function of plant growth (Han & Rowell, 1997; Han et al., 1995). The results are shown in Fig. 4 to 6.

-9- Table 8. Two-Dimensional Average Length of Red Pine Fiber.

Distance from pith Fiber length (mm) at various stalk heights (m) (mm) 0.6 2.3 4.0 5.7 7.2 9.8 10.3 11.7 13.1 Avg 0 2.96 3.18 2.98 3.37 3.51 3.77 2.94 3.06 2.30 3.12 25.4 3.42 3.43 3.39 3.45 3.38 2.89 2.54 2.23 1.43 2.91 50.8 3.26 3.04 2.41 2.66 3.21 2.19 2.11 1.84 - 2.59 76.2 2.69 2.53 2.07 2.62 2.52 1.91 1.25 - - 2.23 101.6 2.08 2.09 1.25 1.17 1.33 - - - - 1.58 Avg 2.88 2.85 2.42 2.65 2.79 2.69 2.21 2.38 1.87 2.53

Table 9. Two-Dimensional Average Length of Aspen Fiber. Distance from pith Fiber length (mm) at various stalk heights (m) (mm) 0.5 2.0 3.5 5.0 6.5 8.0 9.2 10.0 10.9 Avg 25.4 1.24 1.20 1.25 1.07 1.02 1.03 1.43 1.07 1.57 1.21 50.8 1.05 1.09 1.11 0.92 0.80 0.80 0.98 0.96 1.34 1.01 76.2 0.99 1.00 0.94 0.79 0.59 - - - - 0.86 101.6 0.91 0.82 0.81 ------0.85 Avg 1.05 1.03 1.03 0.93 0.80 0.92 1.21 1.02 1.36 1.05

3.3 Distribution of fiber length within plant To determine the distribution of fibers within the plant, a sample of kenaf was pulped and overall fiber length was measured using the Kajaani procedure. The distribution of kenaf core and bast fibers by length is shown in Fig. 7 and 8, respectively. As Fig. 8 indicates, the distribution of bast fibers was normal: maximum fiber length was about 2.7mm, and fiber length ranged from 0 to 8mm.

Fig. 7. Weighted distribution of kraft pulped kenaf Fig. 8. Weighted distribution of kraft pulped kenaf core fiber. bast fiber

3.4 Crystallinity and Permeability Table 10 shows crystallinity values of kenaf as a function of growth. The measurements were taken from core and bast fibers of four different cultivars of kenaf. Crystallinity tended to decrease as the plant matured, but the difference between bast and core fibers was inconclusive (Han & Rowell, 1995). The permeability of some common fibers was measured. Kenaf core had the highest permeability, followed by cotton (Fig. 9).

- 10 - Table 10. Crystallinity of Kenaf as a Function of Growtha. C-108 T-1 E-41 45-9 DAP Fiber Core Fiber Core Fiber Core Fiber Core 56 84.25 78.38 80.77 87.72 78.40 81.08 80.53 82.35 84 78.87 72.13 76.43 73.85 81.48 12.22 77.62 76.92 112 78.91 78.87 73.94 70.63 80.43 71.79 78.32 75.41 140 80.71 72.31 80.29 79.39 78.17 66.93 78.10 68.18 168 73.57 66.93 77.77 65.19 70.90 64.00 74.64 67.19 196 72:34 68.18 72.86 73.11 70.63 69.53 68.38 70.83

a Source : Refernce 3.

Fig. 9. Permeability values of some common nonwood fibers.

Further research is needed to characterize other physical properties of nonwood fibers. such as density. individual fiber strength. and fiber surface chemistry. Information on such properties will be forthcoming at the 1999 American Chemical Society symposium on advances in analytical methodologies in lignocellulosics chemistry.

4. CONCLUSION

Nonwood fibers have tremendous variations in chemical and physical properties. Of particular importance for pulping are fiber length. lignin content. and cellulose content: 1. Fiber length-Nonwood fibers average 8 mm (flax and hemp) and can be as long as 120 mm (ramie). 2. Lignin content-Lignin content of some nonwood fibers is lower than that of high-yield pulp. Hemp contains about 3% lignin and pineapple and samandoque (Hesperaloe funifera) fibers, about 5% lignin. The low lignin content indicates that nonwood fibers will require very mild pulping conditions. 3. Cellulose content-Cellulose content of some non-wood fibers is 80% and higher (cotton, ramie, and hemp). Finally, since most nonwood fibers are annual plants. variations in chemical and physical properties in a given plant might need to be controlled through agricultural practices.

ACKNOWLEDGMENT

The author is indebted to the Korean Society of Wood Science and Technology for the gracious invitation

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